Why leaves change color

Every fall, three things decide how brilliant the color gets: pigments already hiding in the leaf, new pigments some trees make in autumn, and the weather.

Updated September 2026

Green is a mask

All summer, leaves are packed with chlorophyll, the green pigment that turns sunlight into sugar. Yellow and orange pigments called carotenoids are in the leaf the whole time, but the green hides them.

As days get shorter, trees stop making chlorophyll and break down what’s left so they can reclaim its nutrients. The green fades and the yellows and oranges show through. That’s the gold of quaking aspen, paper birch, shagbark hickory, and tulip tree.

Red is made fresh

Reds and purples come from anthocyanins, which some trees make only in fall. As a leaf gets ready to drop, a seal forms at the base of its stem and traps sugars inside. Some of that sugar becomes anthocyanin. One leading idea is that the red works like sunscreen, protecting the leaf while the tree pulls nutrients back out.

This is why red maple, sugar maple, staghorn sumac, black gum, and flowering dogwood can turn so vivid, and why the same tree can look different from one year to the next.

Brown is what’s left

Tannins are brown compounds that remain after the other pigments break down. Oaks and beeches are rich in them, which is why they finish in russet, bronze, and tan. Young american beech and many oaks keep their dry leaves on the branches well into winter.

What sets the timing

Day length is the main clock, which is why peak arrives at roughly the same time each year in a given place. Temperature and moisture fine-tune it. Color starts in the far north and at high elevation, then works south and downhill through the season. In the East, peak comes a few days earlier for every degree of latitude north and every 1,000 feet of elevation you climb. The foliage map uses those patterns to estimate peak for every town.

What makes a great year

The best seasons usually follow a wet spring and summer that keep leaves healthy, then a stretch of warm, sunny fall days and cool nights that stay above freezing. Sunny days build sugar, and cool nights keep it in the leaf, where it becomes red pigment.

Late-summer drought can make leaves brown and drop early. A warm, cloudy fall tends to delay color and mute it. An early hard freeze can kill leaves before they turn, and a strong storm near peak can strip a hillside in one night.

Why leaves fall

The seal that forms at the base of each leaf stem is called the abscission layer. Once it’s complete, the leaf is cut off from the tree and falls with the next breeze. Dropping leaves lets broadleaf trees save water and avoid damage from snow and ice through winter. Most evergreens keep tough, waxy needles instead, with a few exceptions like the tamarack and larch.